Electronics > Projects, Designs, and Technical Stuff
Cutting open tiny filament bulbs
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ChristofferB:

--- Quote from: richard.cs on December 23, 2018, 09:12:22 pm ---For slightly larger lamps (mes indicators) I have found heating a spot on the envelope with a small gas flame melts a hole, doing it with a small enough flame gets just a hole with thickened edges, without the envelope collapsing onto the filament.

Worth a try on these.

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That's a great idea! Letting the vacuum suck in a tiny bubble, definately worth a try.


--- Quote from: jpanhalt on December 23, 2018, 09:25:46 pm ---Water has been mentioned as an aid to spreading a scratch to become a crack.   A little spit works better.   Another trick is to make your fine scratch.   The take a glass rod (2 mm or less) and heat it to make a little red blob on the end.  Then touch it to the crack.  Again, spit helps.   That is a safe was to open evacuated ampules.  When you make a scratch, don't saw back and forth.   That decreases its effectiveness.

Back to your basic problem, glass works entirely differently under water than dry.   I can even demonstrate cutting it with scissors under water.  Grinding is great for cutting glass bulbs under water. 

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Also worth a try. Only issue is that hot glass fuses to cold glass VERY quickly, and the 1/8" tolerances are so tight I can't risk any deformation of the OD.


--- Quote from: Globe Collector on December 23, 2018, 10:24:34 pm ---  Hmmm, TCD for GC....interesting project.

  I'd take the chemical approach. Cover the lamp in wax, scrape away the wax where you want the bulb removed and dunk it into HF and etch the glass away. I'd monitor the filament resistance and detect the change once the HF gets through and use this end point to sound an alarm or activate a solenoid to add a lot of sodium hydroxide or lift the lamp to halt the process to prevent the HF etching through the fine filament. I reckon you would only loose a few lamps in trials to be able to refine the process to be reproducible and reliable.

  All the mechanical methods mentioned above are quite valid...but amazingly difficult to implement on such a small lamp where just holding onto it to take all the reactive forces of dremel blades or WC scratching tools will be an issue in itself not to mention the sheer size of the cutting edges compared to the bulb diameter itself.

  When I saw this post it bought back memories of Chemisrty at Uni. I remember learning about FID's (Flame Ionization Detectors) in an undergraduate lecture and at the end if the lecture I told everybody that I could probably build one out of bits from the junk box...they all "poo-hooed" it as "impossible", which was, of course like a "red rag to a bull". So I built it, i used a nozzle from a disposable cigarette lighter and cut the ends off...and pushed the "jellyroll" out of an axial electrolytic capacitor to get the cylindrical sensing electrode around the flame, I used a high voltage corona wire unit from a photocopier and I recall that the amplifier used a 12AU7 valve as the gain stage because of its high input impedance and immunity to high voltages.  I took it to Uni a few days later and convinced them to let me connect it to the output port of the column in one of the GC's there...it worked just like the "real" thing and they all had to "eat their words".

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That's how I'd do it in my research lab too, but I'm doing this at home. I'm not convinced it would work, as soon as the HF makes a pinhole through the envelope the vacuum would suck the solution in, spraying all internal surfaces, and damaging the filament. HF is pretty expensive too, not to mention unpleasant to deal with.

your FID sounds intrigueing! I was strongly considering doing something similar before settling on the TCD. The GC runs fine with the current detector, though, you should check out my earlier thread on it if you're interested!


--- Quote from: james_s on December 23, 2018, 10:35:11 pm ---I just went and tried this right now since I realized I still had a burned out miniature lamp in my pocket. This took about 10 seconds on my belt sander, it was trivially easy just holding the lamp in my fingers and buzzed the end off. I wouldn't even consider messing around with HF when there's such a simple and easy way of doing it without any nasty chemicals.

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Gotta love christmas decorations, I assume? Thanks for the hands-on, that looks excellent! The finish of the edge isn't very critical, as the seal is made around the diameter of the envelope.


Globe Collector:
 I moved house recently and found that FID while doing so. I had not seen it for 30 years and had forgotten about it, but now, its gone again, all packed away. I really should go and get it out again and post some pictures here.

Yes, I agree that HF is very nasty, so if sanding works, without removing your fingernails or flicking the lamp across the room, then, by all means, use it.
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